The invention relates to a mechanism for compensating the gravitational force acting on a slider of a linear motor, in particular of an electromagnetic direct linear motor, and acting on a load to be carried and moved by the slider, capable of moving along a travel path.
Such linear motors exhibit significant advantages over conventional drives such as servo-motors with belts, step motors with spindles, mechanical disk cams, pneumatic cylinders or mechanical levers. Electro-magnetic direct linear motors consist essentially of two components, namely a fixed stator and a movable slider. These two components are connected by neither drag contact nor cable, in other words, they are electronically contact-free connected. The linear translational lifting movement is therefore generated directly, without mechanical gears, belts or levers, by means of electromagnetic forces, i.e. without additional mechanical elements susceptible to wearing. This enables such linear motors to effect extremely dynamic movements with particular ease and without additional components.
One problem encountered by such linear motors is that when arranged vertically and in a switched off condition, the slider falls down under gravity. A vertical arrangement also causes the working point of the drive to shift unfavourably. In the worst case, the constant force allowed by a vertically arranged linear motor is, due to the development of heat, insufficient to permanently support and move a certain load. The linear motor must then be switched off or cooled down, with considerable expense.
Accordingly, it is a purpose of the invention to create a mechanism to compensate the gravitational force at linear motors, which avoids the aforementioned disadvantages and which is designed simple and compact.
In accordance with the invention, this task is solved by a mechanism for compensating the gravitational force acting on a slider. The mechanism includes a spring element that exerts on the slider an elastic restoring force opposite the gravitational force. Unlike an arrangement which enables the gravitational force to be compensated by a counter-weight, use of the spring element as defined by the invention does not have a negative affect on the dynamics of the system. The purpose of the invention is therefore, with the aid of a spring element connected to the slider and the stator, to achieve compensation of the gravitational force acting on the slider and the load potentially to be supported and moved by it, with the aid of opposing, elastic restoring forces. Determined by this mechanical gravitational compensation, the mechanism can be designed simple and compact and the linear motor can be operated reliably and without interruption over long periods.
Advantageously, the restoring force of the spring element is coordinated with and preferably adjustable to the mass of the slider and the load in such a way that the slider can be brought into a position of balance, wherein the state of balance, of the system is at a desired operating point of the linear motor, when said linear motor is idle.
In this way it is avoided with certainty that the rotor is accelerating up together with the load supported and moved by it, which in turn prevents risk of damage. It is also advantageous if the restoring force of the spring element is set or will be set such that the slider together with ist load is moved, when the linear motor is in an idle state, slowly in the direction of gravity, i.e. in a downwards direction.
It is particularly advantageous if the restoring force of the spring element is essentially constant over the travel path and/or the stroke of the slider. This creates favourable and reproducible operating conditions for the linear motor.
In accordance with a particularly advantageous embodyment of the invention, the spring element is embodied with a torsional or spiral spring, in particular with a spiral flat spring. Such a spring element allows the aforementioned functions in a particularly advantageous manner and allows for a particularly compact design of the mechanism.
This situation can be further improved, if the spiral spring is mounted in a drum rotatable on a rotational axis, wherein the spiral spring is supported at one of its ends against the drum and at its other end against a support component connected to a stator of the linear motor.
Particularly advantageous force transmission and operating conditions can be achieved by a connecting element which can be rolled up and which is attached at one of its ends to the drum and at its other end to the slider of the linear motor. If this connecting element is further embodied as a strip or cable that can be rolled up on an outer periphery of the drum, the force transmission and operating conditions can be further improved.
It is also advantageous, if the support component is attached to an adjusting body, which is rotatable on a rotational axis and which is preferably designed with a housing for receiving the spiral spring and which is lockable against torsion at various positions of angular rotation with the aid of a fixing device. In this way, the zero point of the mechanism, i.e. its position of angle of rotation can be set to precisely the centre of the maximum positioning range of the linear motor, by the adjusting body being rotated preferably manually into the desired position and then in this position, locked against torsion with the aid of the fixing device. A Screw or a bolt have proved to be particularly suitable fixing devices. These can be inserted through and/or screwed into through holes parallel to the rotational axis, in the adjusting body and into openings on the stator side formed for this purpose. These openings are arranged on a radius around the rotational axis, preferably offset to the same distance. An even finer adjustment and proportioning option can be achieved in that several bore holes are arranged around the periphery of the adjusting body, offset by preferably the same distance, for receiving the screw or the bolt, wherein the distances between the bore holes in the adjusting body are designed to be varied and preferably larger than the distances between the bore holes in the support body on the stator side.
A particularly compact arrangement, in particular an axle body (z-axis) of a handling apparatus enabling linear movements in a vertical direction, can be achieved in that the slider, preferably embodied as a coil component for an electromagnetic direct linear motor, receives the stator in the form of a tube or rod and is mounted on it.
It is understood however, that as an alternative, the slider preferably embodied as a magnetic component for an electromagnetic direct linear motor, can also be formed as a tube or rod, which is received and mounted in the stator. In both cases, the linear motor is advantageously embodied as a permanently excited, two-phase synchronous motor. Electro-magnetic direct linear motors also offer the advantage that with the aid of suitable sensors, for example magnetic field and/or hall sensors, an integrated position recording can be achieved.
In accordance with a particularly advantageous application, the invention relates also to a fluid analysis device, in particular for micro-fluid analysis, for example the bio-analysis, i.e. in particular for DNA, RNA and/or protein analysis, with a handling device for samples, for the analysis, removal and/or adding of samples, which contains a mechanism in accordance with one of the claims 1-10.
It is understood that any combination whatsoever of the aforementioned measures are also possible.